1. Field of the Invention
The present invention relates to a tracking traverse control circuit for controlling the track jump operation in a CD player etc.
2. Description of the Related Art
In a CD player, there are often cases of jumping from one track to another track, for example, at the time of going to the start of a music.
In particular, in a CD ROM, it is particularly important in terms of performance that data can be instantaneously retrieved. Therefore, the performance of the optical servo signal processing circuit for processing optical servo signals has important significance.
Optical system servo signal processing circuits for CD players have already been realized by LSIs. At the present time, both analog processing and digital processing types are in general use.
In current general servo systems, circuits for controlling the servo signal processing (servo auto sequencers) are being developed. These sequencers are being controlled by microcomputers.
FIG. 1 is a block diagram of a servo signal control system of a CD player.
In FIG. 1, 1 represents a CPU used as a microcomputer, 2 represents a servo auto sequencer, 3 represents a servo signal processing IC, and 4 represents an optical system.
In such a configuration, when a servo auto sequencer 2 receives an auto sequence command S.sub.1 from the CPU 1, a servo control sequence is started, and a command code and 8-bit serial data are generated for controlling the servo signal processing IC 3 to supply them to the servo signal processing IC 3 as a signal S.sub.2.
The signal S.sub.2 supplied from the servo auto sequencer 2 to the servo signal processing IC 3, more specifically, as shown in FIG. 2, is comprised of the clock signal CLK, data DAT, and latch signal XLT.
The data DAT, as shown in FIG. 4A, is comprised of D0 to D7 8-bit serial code data. The upper four bits "0010" of the 8-bit serial code mean that the command relates to tracking servo and sled servo control. Among the lower four bits at this time, as shown in FIGS. 4B and 4C, the T2 and T1 corresponding to the data D3 and D2 show tracking commands and the S2 and S1 corresponding to the data D1 and D0 show sled commands.
In these tracking commands T1 and T2 and sled commands S2 and S1, "00" is a "servo off" command by which no control signals are generated for the optical system 4.
"01" means "servo on" and forms a normal servo loop.
"10" means "forward direction", that is, is a command for moving from the inner circumferential direction to the outer circumferential direction of the disk.
"11" means "reverse direction" that is, is a command for moving from the outer circumferential direction to the inner circumferential direction of the disk.
The actual operation is performed by the transmission of the above serial commands from the servo auto sequencer 2 to the servo signal processing IC 3.
FIG. 5 is a conceptual view showing the basic configuration of the optical system 4. In FIG. 5 represents an optical disk, and 6 represents a spindle motor.
The optical system 4, as shown in FIG. 5, is comprised by a semiconductor laser 41, a beam splitter 42, an objective lens 43, a cylindrical lens 44, a photodetector 45, a tracking servo mechanism TRK, a focus servo mechanism FOC, and a sled servo mechanism SLD.
In this optical system 4, the laser beam emitted from the semiconductor laser 41 passes through the beam splitter 42 and strikes on the lens 43. The laser light striking on the lens 43 is converged thereat and emitted as a spot of light on a desired track of the optical disk 5.
The spot of laser light emitted on the optical disk 5 is reflected on the optical disk 5 and is returned to the lens 43. This reflected returned light passes through the lens 43 and strikes on the beam splitter 42. The light striking the beam splitter 42 is reflected and strikes on the cylindrical lens 44 where it is converged and received by the photodetector 45.
In the photodetector 45 such as a four division photo detector, the reflected-returned light is converted to an electrical signal of a level in accordance with the amount of received light. This electrical signal is subjected to a predetermined signal processing. As a result, a tracking error signal TE etc. is generated and is fed back to the servo signal processing IC 3. Servo control is performed based on the tracking error signal TE etc.
The servo control covers the tracking servo mechanism TRK, the focus servo mechanism FOC, and the sled servo mechanism SLD. At the time of tracking, however, it mainly covers the tracking servo mechanism TRK and the sled servo mechanism SLD.
The tracking servo mechanism is controlled so that the beam of light from the semiconductor laser 41 of the optical system correctly follows the track, that is, tracking is performed.
The sled servo control mechanism is a servo system for places the optical system 4 on a slider and moves the optical system by the slider to a range which the tracking servo mechanism can cover, since the tracking servo mechanism alone cannot trace the entire surface of the disk in a CD player. Normally, in a sled servo mechanism, the servo control is performed so that the low frequency band component of the tracking servo mechanism becomes 0. The reason is that the tracking servo mechanism lens is always made to operate directly above nearby.
The tracking traverse control of the servo auto sequencer 2 for moving the optical system from the current track to a target track using this servo system is provided with a high precision traverse single-track jump and 10-track jump and poor precision, but short convergence 2N-track jump and M-track move sequences.
FIGS. 6A to 6C, FIGS. 7A to 7C, FIGS. 8A to 8C and FIGS. 9A to 9C are timing charts of the time of a conventional single-track jump, 10-track jump, 2N-track jump, and M-track move.
The signal CNIN shown in these figures is a digitalized form of the tracking error signal TE and is generated in the servo signal processing IC. The inverted busy signal BUSY.sub.-- shows the execution of an auto sequence at the time of a low level. Further, BLIND A is a predetermined time set as the standby time from when the latch signal XLT becomes active at a low level ("low active").
When performing a single-track jump forward, as shown in FIGS. 6A to 6C, a code $48 (reverse is $49) command is received from the CPU 1. Along with this, the latch signal XLT becomes "low active" and the inverted busy signal BUSY.sub.-- becomes the low level. Further, the code $28 command is sent to the servo signal processing IC 3. As a result, a tracking forward kick is performed. Next, when the next rising edge of the signal CNIN is detected, the code $2C command is issued and a brake is energized. After the elapse of the period BRAKE B, a code $25 command is issued and the tracking servo mechanism and sled servo mechanism turn on.
When performing a 10-track jump forward, as shown in FIGS. 7A to 7C, a code $4A (reverse is $4B) command is received from the CPU 1. Along with this, the latch signal XLT becomes "low active" and the inverted busy signal BUSY.sub.-- becomes the low level. Further, the code $2A command is sent to the servo signal processing IC 3. As a result, a tracking forward kick is performed.
Next, after the elapse of the period BLIND A, five of the next trailing edges of the signal CNIN are counted. When five are counted, a code $2E command is issued. As a result, a tracking reverse kick is performed and a brake is applied to the tracking actuator. The fact that the speed of the actuator has become sufficiently slow is detected, a code $25 command is issued, and the tracking servo mechanism and sled servo mechanism are turned on.
The detection of the speed of the actuator becoming sufficiently slow is performed by detecting when one cycle of the signal CNIN becomes longer than a preset overflow C.
When performing a 2N-track jump forward, as shown in FIGS. 8a to 8c, a code $4C (reverse is $4D) command is received from the CPU 1. Along with this, the latch signal XLT becomes "low active" and the inverted busy signal BUSY.sub.-- becomes the low level. Further, the code $2A command is sent to the servo signal processing IC 3.
This 2N-track jump is basically the same in sequence as the 10-track jump, but differs in the fact that after the tracking servo mechanism is turned on, the sled is continued to be moved for exactly the time KICK D.
When performing an M-track move, as shown in FIGS. 9A to 9C, a code $4E (reverse is $4F) command is received from the CPU 1. Along with this, the latch signal XLT becomes "low active" and the inverted busy signal BUSY.sub.-- becomes the low level. Further, the code $22 command is sent to the servo signal processing IC 3. Due to this, just a sled forward kick is performed. Next, after the elapse of the period BLIND A, M number of the signal CNIN are counted. When M number are counted, a code $25 command is issued and the tracking servo mechanism and sled servo mechanism are turned on. In this way, the M track move adopts the system of moving just the sled and is suitable for large moves of several hundreds to several tens of thousands of tracks.
However, in the above-mentioned tracking traverse control, while various modes are provided and anything from single-track jumps to major track movements of several hundred to several thousands of tracks are possible, small movements of relatively small numbers of track traverses are high in accuracy, but inaccurate as to the number of tracks traversed, so in the end a repeat traverse becomes necessary for correction and as a result a long time ends up being taken until the target track is reached. Contrary, large movements of more than several hundred track traverses are problematic as to precision though the jumps of several hundred tracks etc. can be ended in a short time. That is, in the past, a high speed seek operation was difficult since there was no sequencer precision in a short time.
Further, in the above-mentioned tracking traverse control, the sled was not controlled in accordance with the state of the traverse, so when the traverse involved more than several hundred tracks, with the sled stopped in state, the range of controllable tracking ended up being exceeded.
Further, at the time when starting a traverse, the sled is unstable in the start of operation due to static friction. Further, it suffers from the disadvantage that a long time ends up being taken until the set speed of traverse is reached in the tracking.